Method of detecting presense of an object using a time of flight sensor

Abstract

A method can be used to detect the presence an object within a field of view of a time-of-flight sensor. A histogram generated by the time-of-flight sensor is obtained. The histogram includes a number of bins associating a number of detected photons to a given acquisition time. A portion of the bins of the histogram is transformed into points in a transformed domain that features a first area containing only points associated to bins representative of the presence of the object and a second area having only points associated to bins not representative of the presence of the object. The bins of the histogram representative of the presence of the object are identified from the points located in the first area.

What is claimed is: 
     
         1 . A method for operating a time-of-flight sensor, the method comprising:
 emitting optical radiation from the time-of-flight sensor toward an object;   detecting, by the time-of-flight sensor, photons from a reflection of the optical radiation from the object;   obtaining a histogram generated by the time-of-flight sensor, the histogram comprising a plurality of bins associating a number of the detected photons to a given acquisition time;   detecting a main bin representative of a presence of the object, the main bin having the largest number of detected photons among the bins of the histogram;   transforming a portion of the bins of the histogram into points in a transformed domain featuring a first area containing only points associated to bins representative of the presence of the object and a second area having only points associated to bins not representative of the presence of the object, wherein transforming the portion of the bins of the histogram in a transformed domain comprises plotting a scatter graph, wherein each point in the scatter graph is associated to a bin of the histogram, each point being disposed according to a difference between the acquisition time of the bin associated to this point and the acquisition time of the main bin, and according to a ratio between the number of the detected photons for the main bin and the number of the detected photons for the bin associated to this point; and   identifying the bins of the histogram representative of the presence of the object from the points located in the first area.   
     
     
         2 . The method according to  claim 1 , wherein the transforming concerns only bins that follow the main bin in the histogram. 
     
     
         3 . The method according to  claim 1 , wherein identifying the bins representative of the presence of the object comprises:
 comparing positions of the points in the graph with respect to a threshold function variable according to the acquisition times of the bins;   defining a limit between the first area and the second area of the transformed domain; and   selecting a bin as a bin representative of the presence of the object according to the result of the comparing.   
     
     
         4 . The method according to  claim 3 , wherein the threshold function variable defines a segment;
 wherein the positions of the points are compared with respect to the segment of the threshold function; and   wherein a bin is selected as a representative bin when the point associated to this bin is located in the graph on one side of the segment in the first area.   
     
     
         5 . The method according to  claim 4 , wherein the segment is obtained from a slope coefficient and origin coordinates stored in a memory of the time-of-flight sensor. 
     
     
         6 . The method according to  claim 4 , wherein selecting the bin comprises selecting a plurality of bins and wherein the threshold function variable defines a plurality of segments. 
     
     
         7 . The method according to  claim 1 , further comprising, prior to the transforming, determining bins of the histogram that are potentially representative of the presence of the object, the transforming being performed only for these bins. 
     
     
         8 . A time-of-flight sensor comprising:
 an emitter configured so as to be able to emit optical radiation toward an object;   a receiver configured so as to be able to detect photons from a reflection of the optical radiation from the object;   a processing unit configured so as to be able to:
 plot a histogram from the number of photons detected by the receiver at several successive acquisition times, the histogram comprising a plurality of bins associating a number of detected photons to a given acquisition time; 
 detect a main bin representative of a presence of the object, the main bin having the largest number of the detected photons among the bins of the histogram; 
 transform a portion of the bins of the histogram into points in a transformed domain that features a first area containing only points associated to bins representative of the presence of an object and a second area having only points associated to bins not representative of the presence of the object, wherein the portion of the bins of the histogram is transformed into the transformed domain by plotting a scatter graph, wherein each point in the scatter graph is associated to a bin of the histogram, each point being disposed according to a difference between the acquisition time of the bin associated to this point and the acquisition time of the main bin, and a ratio between the number of the detected photons for the main bin and the number of the detected photons for the bin associated to this point; and 
   identify bins of the histogram representative of the presence of the object from the points located in the first area.   
     
     
         9 . The sensor according to  claim 8 , wherein the processing unit is configured to perform the transforming only for bins that follow the main bin in the histogram. 
     
     
         10 . The sensor according to  claim 8 , wherein the processing unit is configured to identify bins representative of the presence of the object by:
 comparing positions of the points in the graph with respect to a threshold function variable according to the acquisition times of the bins and defining a limit between the first area and the second area of the transformed domain; and   selecting at least one bin as a bin representative of the presence of the object according to the result of the comparing.   
     
     
         11 . The sensor according to  claim 10 , wherein the threshold function variable defines at least one segment, the processing unit being configured to identify bins representative of the presence of the object by:
 comparing the positions of the points in the graph with respect to the segment of the threshold function; and   selecting a bin as a representative bin when the point associated to this bin is located in the graph on one side of the at least one segment in the first area.   
     
     
         12 . The sensor according to  claim 11 , further comprising a memory storing a slope coefficient and origin coordinates that enable the processing unit to establish the segment. 
     
     
         13 . The sensor according to  claim 8 , wherein the processing unit is configured to determine, prior to the transforming, bins of the histogram that are potentially representative of the presence of the object, the transforming being performed only for these bins. 
     
     
         14 . The sensor according to  claim 8 , wherein the processing unit comprises a histogram processor and a processor;
 wherein the histogram processor is configured to plot the histogram from the number of photons detected at several successive acquisition times; and   wherein the processor is configured to receive the histogram from the histogram processor, transform the portion of the bins of the histogram into points in the transformed domain and identify the bins of the histogram representative of the presence of the object.   
     
     
         15 . A time-of-flight sensor comprising:
 an emitter configured to emit optical radiation toward an object;   a receiver configured to detect photons from a reflection of the optical radiation from the object;   a processing unit; and   a memory coupled to the processing unit and storing software that, when executed by the processing unit, causes the processing unit to:
 obtain a histogram generated by the time-of-flight sensor, the histogram comprising a plurality of bins associating a number of the photons detected by the receiver to a given acquisition time; 
 detect a main bin representative of a presence of the object, the main bin having the largest number of detected photons among the bins of the histogram; 
 transform a portion of the bins of the histogram into points in a transformed domain that is defined from the main bin, the points featuring a first area containing only points associated to bins representative of the presence of the object and a second area having only points associated to bins not representative of the presence of the object, wherein the portion of the bins of the histogram in a transformed domain are transformed by plotting a scatter graph, wherein each point in the scatter graph is associated to a bin of the histogram, each point being disposed according to a difference between the acquisition time of the bin associated to this point and the acquisition time of the main bin, and a ratio between the number of the detected photons for the main bin and the number of the detected photons for the bin associated to this point; and 
 identify the bins of the histogram representative of the presence of the object from the points located in the first area. 
   
     
     
         16 . The sensor according to  claim 15 , wherein the software causes the processing unit to identify the bins representative of the presence of the object by:
 comparing the positions of the points in the graph with respect to a threshold function variable according to the acquisition times of the bins;   defining a limit between the first area and the second area of the transformed domain; and   selecting a bin as a bin representative of the presence of the object according to the result of the comparing.   
     
     
         17 . The sensor according to  claim 16 , wherein the threshold function variable defines a segment;
 wherein the positions of the points are compared with respect to the segment of the threshold function; and   wherein a bin is selected as a representative bin when the point associated to this bin is located in the graph on one side of the segment in the first area.   
     
     
         18 . The sensor according to  claim 17 , wherein the segment is obtained from a slope coefficient and origin coordinates stored in the time-of-flight sensor. 
     
     
         19 . The sensor according to  claim 17 , wherein the software causes the processing unit to select the bin by selecting a plurality of bins and wherein the threshold function variable defines a plurality of segments. 
     
     
         20 . The sensor according to  claim 15 , wherein the software further causes the processing unit to determine bins of the histogram that are potentially representative of the presence of the object prior to the transforming, the transforming being performed only for these bins.